From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mga01.intel.com ([192.55.52.88]:49466 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725866AbeICNFG (ORCPT ); Mon, 3 Sep 2018 09:05:06 -0400 Subject: Re: [PATCH] media: intel-ipu3: cio2: register the mdev on v4l2 async notifier complete To: Javier Martinez Canillas , linux-kernel@vger.kernel.org Cc: Mauro Carvalho Chehab , Tian Shu Qiu , Jian Xu Zheng , Sakari Ailus , Yong Zhi , Bingbu Cao , linux-media@vger.kernel.org References: <20180831152045.9957-1-javierm@redhat.com> From: Bing Bu Cao Message-ID: Date: Mon, 3 Sep 2018 16:49:50 +0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-media-owner@vger.kernel.org List-ID: On 09/03/2018 03:35 PM, Javier Martinez Canillas wrote: > Hi, > > Thanks a lot your feedback. > > On 09/03/2018 09:25 AM, Bing Bu Cao wrote: >> >> On 08/31/2018 11:20 PM, Javier Martinez Canillas wrote: >>> Commit 9832e155f1ed ("[media] media-device: split media initialization and >>> registration") split the media_device_register() function in two, to avoid >>> a race condition that can happen when the media device node is accessed by >>> userpace before the pending subdevices have been asynchronously registered. >>> >>> But the ipu3-cio2 driver calls the media_device_register() function right >>> after calling media_device_init() which defeats the purpose of having two >>> separate functions. >>> >>> In that case, userspace could have a partial view of the media device if >>> it opened the media device node before all the pending devices have been >>> bound. So instead, only register the media device once all pending v4l2 >>> subdevices have been registered. >> Javier, Thanks for your patch. >> IMHO, there are no big differences for registering the cio2 before and after all the subdevices are ready. >> User may see a partial view of media graph but it presents what it really is then. >> It indicate that device is not available currently not it is not there. > I disagree that there are no differences. The media graph shouldn't be exposed > until its complete. That's the reason why we have a v4l2 async notifier .bound > and .complete callbacks (otherwise the .bound would be enough). > > It's also the reason why media register was split in _init and _register, as I > mentioned in the commit message. I revisit the commit 9832e155f1ed and understand and agree that. Seems like there are some other drivers (such as rcar-vin and omap4iss) still have similar issues. >> Could you help tell more details about your problem? The full context is helpful for me to reproduce your problem. > If an application opens the media device node, how it would know that has an > incomplete media graph? how it would know once the subdevice has been .bound > and that has to query the media graph again? > > AFAIK there's no way to notify that information to user-space currenctly but > I may be wrong. > > Best regards,